When designing and configuring any cellular or wireless communication network, several aspects have to be taken into account. The cellular communication networks of today are experiencing increasing amount of traffic, posing hard requirements on the cellular network.
One problem in cellular communication networks is interference between cells, also called inter-cell interference. Typically, one cell has a plurality of neighbouring cells. All these cells cause interference between each other.
One approach to reduce interference between cells is to let different cells make use of different frequencies compared to its immediate neighbours. However, such an approach requires a large spectrum of different frequencies. A cellular communication network typically has a relatively limited frequency band to use, hence this approach may not be possible to implement.
Another approach to reduce or eliminate inter-cell interference is to make use of Inter-Cell Interference Coordination, ICIC. ICIC is introduced into the Long Term Evolution, LTE, protocol to improve cell edge performance. ICIC divides the frequency resources in a cell into several parts, typically between a cell edge area and a cell centre area. Neighbouring cells are then not allowed to use the same frequencies at their respective cell edge area.
In order to employ ICIC, the radio base station of the cell must be able to determine where in the cell the UEs are located in order to schedule appropriate frequency resources to the different UEs.
One approach to determine the location of a UE in a cell is the distance method. In this approach, the cell is approximated to a circle having a radius R. Then the boundary between the cell centre and the cell edge is defined as a factor of the radius. Typically, the boundary is about (0.7-0.8)R such that the cell centre area is from 0*R up to say 0.75*R and the cell edge area is from 0.75*R up to R.
This approach is associated with different problems. The distance from the cell centre to the UE is difficult to determine. The distance can be estimated using e.g. a path-loss shadow fading model but such a model is influenced by many factors and cannot estimate distances without substantial computation complexity. Another way to estimate the distance is using Global Positioning System, GPS. However, this way lacks compatibility with UEs not being equipped with GPS. Further the accuracy of GPS may vary depending on the environment and may not always be accurate enough in urban environments.
Another approach to determine the location of a UE in a cell is the Single Reference Signal Received Power, RSRP, method. In this approach, the radio base station uses the RSRP values reported from the UE to determine the location of the UE. One threshold is defined such that the location of the UE is determined by the reported RSRP value being above or below the defined threshold.
Also this approach is associated with some problems. One problem is if the UE is moving around in the cell such that the reported RSRP values from the UE are close to the RSRP threshold value. This might lead to oscillating handovers between cell edge are and cell centre area. Single RSRP values may also vary due to the environment and may therefore not be reliable.